Weighing cells, particularly of the kind used in electronic balances, can be calibrated in different ways. The balance is in many cases equipped with an internal calibration weight which can be coupled to the force-transmitting mechanism of the weighing cell through a suitable linkage. An internal calibration weight is normally used only to perform calibrations. In the normal measuring mode, the internal calibration weight has no contact with the force-transmitting mechanism.
As another possibility, separate or external calibration weights can be used which are placed on the load carrier of the weighing cell. The placement of the calibration weights should be reproducible and very precise, so as to ensure that all calibrations take place under comparable conditions. External calibration weights are used for example for weighing cells that are specially designed to save space, so that there is no room for a calibration weight inside the balance housing, or for weighing cells of particularly rugged construction for use in harsh environments, because an internal calibration weight could not be moved with the necessary precision under such conditions.
With external calibration weights, it is also possible to perform multipoint calibrations using a set of calibration weights. A calibration weight set consists of a plurality of certified calibration weights which are weighed in sequence one after another.
To prevent a change of the mass of calibration weights over time, they should be stored in a way that minimizes any accumulation of dirt or dust on them. Also, calibration weights should always be picked up and held with suitable utensils such as tweezers, gloves, or a robot, so that for example no skin grease or other contamination can be transferred to the calibration weight by the user, which would cause a change in the mass of the calibration weight. These measures should be observed all the more strictly the smaller the mass of the calibration weight is that is being used.
The measures just described are relatively easy to implement for weighing cells which are used in a stand-alone balance. However, in situations where compact weighing cells are used either individually or in large numbers, for example as a weighing cell array in a process system or plant, it gets difficult to use external calibration weights, on the one hand because space is limited, and on the other hand the conditions for storing and using the calibration weights are not always optimal. Furthermore, an individual weighing cell and/or the load carrier belonging to it can be removed from the weighing cell array only through a laborious process. If the weighing cell is used to measure not only discrete solid objects but also free-flowing substances, the load carrier, in the process of being filled, can become contaminated, and the contamination can be transferred, in turn, to a calibration weight that is used for example to verify the calibration of the weighing cell.
Thus, the object of the invention lies in developing a device whereby a weighing cell can always be calibrated easily, quickly and with high precision with an external calibration weight.